And edward  p



. overcoolcin Patented Dec. 6, 1927.

UNITED STATES res ns PATENT OFFICE.

LINN BRADLEY, OF IVION'ICLAIR, NFAV JERSEY, AND EDWARD P. MCKEEFE, OF NEW YORK, N. Y.

MANUFACTURE OF PULP AND PAPER.

No Drawing. Application filed February This invention relates to improvements in the commercial manufacture of pulp and paper it'ron'i wood, and includes improvements in the production of the pulp and paper, as well in the pulp and paper themselves. The invention also includes a regenerative process of pulp manufacture in which the residual liquors are treated for the regeneration of cooking liquors for use in the further carrying out of the process.

in the ordinary soda process so-called of manufacturing pulp from wood, the wood cnips are cooked with a cooking liquor consisting essentially of caustic soda. In order to complete the cooking: operation, the amount of the caustic soda required is such that a considerable part of the wood fibres are injured or destroyed or over-cooker, with a corresponding decrease in yield and quality of pulp produced. It the soda process is carried out with an amount of caustic soda which does not materially injure the fibres, the operation is unreliable or incomplete and the product is unsatisfactory. It, for any reason, the cooking operation is run overtinr as, for example, where a breakdown has occurred in some part of the pulp milL' or in case of delay or an accumulation of pulp in some part of the mill, such that a digester cannot be discharged until the accumulated pulp has been worked oil", the overcooking of the digester charge, with the usual soda cooking liquors, may result in and injury or destruction such that the pulp is or decreased value and reduced yield and may even be dillicult. to handle. The overcookine' of the pulp may cause a partial gelatiniaation ot' the fibres or may maize the pulp more mushy and more ditticult to wash and dry and handle in its subsequent i'uanipulatirm in the pulp mill. Qvercoolting. in the case oi ordinary soda cool-ting; liquors. may not only give ditl'icully in the treatment of the pulp, but may lil cwise give ditliculty in the treatment of the residual, liquors, which contain an increased amount of dissolved fibres.

The pulp produced by the soda process, example, from poplar (aspen) wood, is ilowlsh or brownish in tint, and, the cached pulp on heating, generally turns yellows The pulp is often of a mushy wuich is ditlicult to handle satis- I pulp mill. The pulp made 8, 1922. Serial N0. 535,034.

by the soda process, for example, from poplar (aspen) wood, has been of such inferior properties that it has been considered and used as a short fibre filler in admixture with long tibre pulp which gives strength to the resulting paper. For example, in the manufacture of paper, it has been customary to use from about 50 to 70% of long fibre sulphite pulp (e. g. produced from spruce wood) in admixture with from 50 to 30% of soda pulp made from poplar wood, depending upon the weight and strength of the paper (e. book and magazine paper) to be nmnut'actured. In order to produce such a composite paper it has been customary tor a soda pulp and paper mill either to buy sulphite pulp to admix with the short fibre soda pulp, or to operate bot-h the soda and the sulphite processes independently to produce the respective soda and sulphite pulps, so that the long fibre sulphite pulp could be mixed with the short librc soda pulp, the soda pulp being considered merely a filler, and the sulphite pulp icing relied upon to give strength.

When long fibre sulphite pulp is thus admixed with soda pulp, it is customary to subject the mixed fibres to a beating oper ation in order to convert the sulphite fibres into the proper condition. This beating operation may overheat the setter soda pulp fibres, particularly with a pulp of mushy character which has insufficient strength to withstand the beating operation, and this overheating may further injure the fibres and cause them to fill the voids ot' the pulp and paper in such a way as to injure the felting properties or the subsequent hanrllingz of the pulp and paper.

Owingto the delicacy of the ordinary soda process, it is difficult, even in a wellregulatcd mill, to keep all parts of the pulpmaking process in balance, so that the successive parts ot the process can operate in sequence and on a regular schedule, and ditliculties frequently arise on account of imperfect operating conditions. For example, in the case of a pulp which'is difficult to drain or to bleach, the slowing up of the drainers or bleachers may hold up the digesters a longer time than required for the completion of the cooking operation, thus preventing the blowing off of the digesters un il the part of the mill ready to receive the charge has been freed from the previous charges, with resultii'ig overcooking; of the pulp and injury thereto.

According to the n'esent invention, the ddlicultics and disadnutagcs oi' the ordinary soda process arelargely overcome or minimized and the cooking or the wood in the digesters is arried out in a raw and improved way which gives a superior pulp and paper, which enables the residual liquors to he treated in a more advantageous way, and which enables the mill to be more readily balanced. and to be operated in a more reliable way. The nature and advantages of the invent-ion will more tully appear from the following more oetailed description of the invention.

Accoroing to the present invention, the cooking operation is carried out with a coolilug; liquor consisting; essentially oil? caus soda together with normal sodium sulphiie, with the -au. ;ic soda present in preponeerating amount, that is, with the amount of sodium present as sulphite not exceet inc; the amount of sodium present as *austic hoda, and ordinarily with the ainoitint oi siiodiuin sulphitesmaller in sodiun'i content than that of the caustic soda, for example, from 10 to 525 7g. oi? the total sodium present or somewhat more. The caustic soda, although in prcpondc-rating amount, is nevertheless so controlled lll amount and concentration .21

generation ot the cooking liquors, even by the ordinary procediu'e and apparatiu en ployed iu the treatn'ieut of black liquors our the soda procc (provided the flour; are specially regulated) and even l'l'iou'; the re ual liquors and cooking liquors (.f the present invention ontain a considerable amount of sulphite.

The process of the pres-en iuventir more or less general application. particular value for the treatment 0 he i readil r handleo Ti tlowr and freer WOiiill' niill than the ordinary soda pulp, drains more freely, wishes quicker, bleaches more czu-iily, truer :troin ohjectioinible propertie:-; such as inushiness or a hydrated or gelatinous character, and, as above stated. give; a paper of superior strei h and properties cveu without admixture of long lihre sulphite pulp.

lbie process is also applicable to other woods than poplar, for example, to hard woods or deciduous woods such birch, beech and maple, as well as coniferous Woods 1 opcratipu. The chips suitably 11 Jared, may be charged into the digest ere in in: ch the usual. way, for example, by first i u sing; part of the chips, then introducr it the chips and liquor einiultaneously while my the chip level above the liquor level,

k. and turning on ieain to heat th liquor, drive out Elli, and compact the chips.

'i l' o coolci ute iouor liquor, {S

C0: sistir above stated. is a. essentially of normal sodium sulpl. ite so Y liquor combines the reagents soda process and of the sul- "hough the liquor 's not acid i in the acid sulphite process) x is it as strongly alkaline as the liquor the ordiniuy soda process. By reducing tile amount of caustic coda and suliistituting normal sodium sulphite therefor. we have i the objections and dilliculties 01 21v soda 'irt ccm; are very largely The cooking); liquor uuiy. for c :-;ti.'eu;rth of he ileum 1 un to 61) '3 per lit-er and from 10 er liter oi i'iorniul tlJOdlllll'l sul- ,h an even larger amount of an'i'iurit equal to that ol soda um li ith dense coil. 1 i lly ill(ill.tl.tit(l amount oi ud be used and it is one ientioi that such inus hereinafter cooking liquor in the first instance may be made in anysuitahle way, :tor cs2 ample, by eddi sul. hur di: a suitable solution of cum. a suitable sanction of sodium co:

bcrore miratlcililo zation. The composite cooking liquor may also be made. in a simple and advantageous way, from the ordinary soda and sulphite liquors used respectively in the soda and acid sulphite processes. Where acid calcium sulphite liquors are amilablethey may be made to react with alkaline liquors, with precipitation of neutral calcium sulphite which may be returned to the absorption towers of the sulphite process or otherwise utilized, e. g. with sodium acid sulphate to form sodium sulfite and calcium sulfate or gypsum.

In continued operations, it is only necessary to provide a sufficient amount of the reagents to make up for losses in the process, inasmuch as the cooking liquors can be read; ily regenerated from the residual liquors. in a manner hereafter more fully described.

The following specific example will further illustrate the invention as applied to poplar wood: Three and tln'ee-fourths cords of wood chips, (i. e. 8 cords measured before chipping) made up of about 90% poplar wood and 10% bass wood were charged into the digester together with about 460 cubic feet of cooking; liquor containing 1515 pounds of caustic soda. and 188 pounds of sodium sulphite, together with small and incidental amounts of sodium carbonate (resulting from incomplete eausticizing) and of sodium sulphide (incidentally produced in the regenerating OPEHlLlOH). Small amounts of sodium sulfide, incidentally produced duringthe regenerative process, are advantageously present in the cooking liquor, giving a composite cooking liquor containing caustic soda in preponderating amount, together with sodium sulfite and sodium sulfide. The digester was about 7 feet inside diameter and about 25 feet in height over all. The digester was heated by the direct introduction of steam into the bottom of the digester. About. two hours was required to bring; the digester to pres sure and the charge was cooked for a period of four hours under a steam pressure of 110 to 120 pounds some of the air and seam at the top of the digester being relieved from time to time to promote the circulation and distribution of heat in the (ilig-ester. The charge was then blown from the digester to the blow pit. then conveyed to a storage tank with a perforated false bottom where the liquor was drawn off and the pulp wash-ed by displacement. the residual liquor and the concentrated wash water being conveyed to a storage tank for concentrated liquor. and the dilute wash water being separately stored and used to wash out the blow pit.

The above example is typical for poplar wood, but the specific conditions of this example are capable of variation. For example, instead of circulating the liquor by a steam jet at the bottom of the digester, circulation can be effected by means of a pump.

In the cooking operation, a considerably less amount of the wood goes into solution than in the ordinary soda process. This results in an improvement both in the amount and properties of the pulp and in the com position and treatment of the residual liquors. Because of the increased amount of pulp produced, the storage tanks and ap paratus employed in the subsequent treatment of the pulp may require to be somewhat increascd in their rapacity as compared with appa 'atus employed in treating ordinary soda pulp. Lower yields of pulp generally will be produced with older woods than with green sound wood. The wood may vary somewhat in its water content. and due allowance should be made for this in carrying out the'process. Ordinary poplar wood used by us contained about 15 to 20% of water, and the above example refers to wood of such a water content. IVhcre the wood has been in the water for a considerable time. its moisture content may he as high as 50% or higher.

One of the important advantages of the cooking process of the present invention is that moderate overcooking of the charge in the digester does not injure the pulp to any objectionable extent. so that over-cookingmuch less objectionable than in the ordinary soda process.

Another important and characteristic ad vantage of the invention is that a consider-- ably increased yield of pulp can be produced from the wood than is produced in the ordinary soda process. In the case of poplar wood, for example, this increase may amount to 10% or'more, while the pulp itself will be of greatly improved properties which distinguish it from ordinary soda pulp. Where, for example, a yield of about 1050-1100 pounds of air dry pulp is obtained from a cord of poplar wood according to the ordinary soda process, a yield of around 1200 or 1300 pounds or more of pulp (air dry) can lie-readily produced according to the im-- proved process of the present invention; while the pulp will also be a superior pulp which can be more readily handled and which can be used for purposes and with ad vantages which distinguish it from ordinary soda pulp. The pulp is more uniform and is freer running through the mill. The pulp is characterized by increased fibre strength. freedom from objectionable mushiness. and contains fibres having physical and chemical properties and characteristics which distinguish it from the ordinary soda pulp produced from the same wood.

In its subsequent treatment by draining, washing, screening, thickening, bleaching. etc., the pulp is freer than ordinary soda pulp and can be more readily handled and with less difficulty. The pulp an be bleached and the bleached pulp has superior properties. The spent bleach-liquor can be removed in any suitable way and the bleached pulp can then be converted into sheets and dried or conveyed to the paper mill and used for the manufacture of a superior paper. For the manufacture of unbleached pulp or paper, the bleaching can be omitted. When the pulp is being subjected to. beating, the beater-s can be operated with considerably less power than when the usual mixtures of ordinary soda pulp and sulphite pulp are treated. The new pulp can also be more readily freed from water when subjected to squeezing between rolls in the manufacture of pulp or paper sheets therefrom. In the drying of the pulp, or paper made therefrom, less heating is required than in the case of ordinary soda pulp. The water appears to be held in the pulp in a different way from that in which it is held in or dinary soda pulp. In particular, the water seems to be held in such a way that it comes away from the fibres more readily, perhaps due to the fact that the fibres are not gelatinized or hydrated to such an extent and do not contain so much water intimately combined therewith, as in the case of ordinary soda pulp.

The advantages of the new pulp are par ticularly marked when the pulp is used for the manufacture of paper. The pulp (bleached or unbleached), after screening, thickening'and beating. and after the addition of chemicals or fillers (e. alum, sizing, coloring material, fillers, etc.,) can be run through the refining engine or Jordan engine and then to the paper machine. For the heavier weights of paper, it possible to make excellent book or magazine paper entirely of poplar pulp, without admixture of long fibre sulphite stock. Owing to the absence of admixed sulphite fibres, the stock does not require as much beating as is required by the ordinary adn'iixtures of sulphite and soda pulps, a light brushing in the boaters usually being sufficient. After the refining operation the pulp can be run through the stock chest and then onto the paper machine in regulated amount to give paper of the desired weight. The paper sheet can be formed in much the usual we but the sheet dries easier and with l shrinkage than. ordinary mixed soda and sulphite paper. For example, where previously it was necessary to use a steam pr sure of 18 pounds on the drying rolls of the paper machine, it was found sufiicient to use one and one-half pounds of steam pressure on the same dryer in dryingthe improved paper of the'present invention (made for example from poplar wood). The water can more readily be squeezed out of the sheeton thev squeeze rolls, and the remaining water can more readily be removed on the heated drying rolls. The new paper can also be formed more rapidly, owing to the increased speed at which it can be dried. in one instance, in the case of a S)? pound paper, the paper was dried at the rate of about 115 feet per minute or about ll) feet faster than paper made from admixed soda pulp of ordinary grade and sulphite pulp.

The pa aer also shrinks less in drying on the paper machine, thus making it possible to cut sheets of increased width from the paper. The paper is also more uniformly formed and is strong enough to stand additional pressure if necessary at the calen ler rolls, so that it can be given a softer finish and a higher finish if desired.

The improved paper of the present inv' tion made, for example, from poplar wood, is of particular value for use as book where a soft pliable, durable paper sired which will lay flat and which will pi without fuzzing or the raising of the fibre. It has a characteristic sheen or velvety finish and a surface which readily takes a furl and which can be erased without ising the fibre. It has a characteristic bright 6315; or brilliancy of color. Owing to the more uniform character of the sheet, and the fact that it ooes not shrink as much in drying". the sheet is much safer on the paper mac me and there is less danger of breakage and ill-- terference with continuous operation.

The advantages of the new paper are illustrated by a comparison of it with ordinary book paper made from admixed soda pulp (poplar) and sulphite pulp (spruce). Heretofore in order to make paper of sutiicient strength, at least about 30% of long fibre sulphite pulp was required in the case of the heavier weights of paper, such as pound stock, while 70% of sulphite pulp was com-- monly used in lighter paper, such as 40 pound stock. With the new pulp, however, it has been found possible to omit entirely the admixture of long fibre sulphizte pulp for making the heavier weigl'its of paper. For example, a 70 pound paper made eutirely of the new pulp (from poplar wood) was found, when tested in a Mullen tes r. to have a breaking strength of pound as compared with a breaking rength of 2% pounds for a paper of the no weight made from admixed soda and sulphite pulp according to methods heretofore commonly used. (In referring to a T0 poiuid paper we mean that a ream of 500 sheets of the paper of a standard size of 9.5 )1 3S weighs 70 pounds.)

The paper, when made entirely of pulp, produced accordingto the present invention, for example, from poplar wood, will be of a. substantially uniform character in the sense that it will be made up entirely of fibres of substantially uniform length and properties,

as distinguished from paper made up of llt) til

fibres that have been broken down by over cooking (e. by the ordinary soda process) or by overheating of the soft fibres of the soda process, due to the beat ng of the admixed long fibre sulphitie pulp in admixture with the short fibre soda pulp. One important characteristic of the new pulp and ot' the paper male therefrom is that a minimum of heating is required to convert the pulp into a suitable form for paper making so that the fibres ot the paper are not injured to an objectionable degree by the beating operation, while they are of such an improved character, in composition and properties, that they undergo such beating as is necessary withoutany material breaking down of the fibres, so that the fibres in the finished paper are essentially those of the original wood, as modified by the cook ing and bleaching operation which separates the non-fibrous constituents, and by the mild beating operation which completes the treat ment of the fibres for paper making purposes. In so far as we are aware, we are the first to produce an improved paper of this character, made up entirely of what is commonly considered short fibre pulp, but which is of such superior quality that it enables a superior paper to be produced solely from such short fibre material. When longer fibres are admixedwith the short fibre pulp, in the manufacture of paper, a greatly reduced amount of long fibres can be used and these will not require. any extended treatment in the heaters. The paper in this case will still be, made up, for the most part, of the uniform short fibre pulp of superior character with the longer fibres admixed therewith.

It is one advantage of the present invcntion that it enables ditierent woods to be cooked in admixturewith each other and a satisfactory mixed pulp directly produced. In this case, the resulting pulp and the paper made therefrom will still be made of .tibres of uniform character, since the fibres of the ditterent woods, although diti'cring from each other, will nevertheless be of subs-tam tially uniform character so far as the libres of each wood are concerned.

As an example of the application of the invention to the treatment of mixed woods. we may mention the cooking of poplar wood (which may be admixed with a small amount: of bass wood) with a regulatal amount of spruce wood. The amount of spruce wood ordinarily will be small, say 5 to 10% or even less, although more can be used where an increased admixture of long fibre pulp is desired. In the cooking of such a mixture of woods, the procedure will be similar to that above described in connection with the treatment of poplar wood, although both the pulp and the residual liquors will be modified, due to the dii'l'ercnt character of the admixed spruce fibres of the pulp and to the somewhat different character of the nonfibrous constituents produced from this spruce wood.

As another instance of the application of the invention to the treatment or mixed woods, we will mention the treatment of poplar wood with the addition or admixture ot a small amount of other hard woods, and particularly of hard woods of considerably increased weight or density, such as birch, beech and maple, either separately or in combination. These heavy hard woods contain a greatly increased weight of both pulp fibres and non-fibrous material, so that for equal quantities of wood (by volume) the amountof pulp produced and also the amount of soluble constituents requiring removal in the residual liquors will be correspondingly increased. )Vhere the admixtures oi these dense hard woods is only to the extent ot a few per cent, say up to 5 or 10%, this increased amount or both fibres and non-fibrous constituents will not require any great variation in the process, although the amounts of reagents used in the cooking liquor can be somewhat increased to take care of the increased amount of non-fibrous constituents to be dissolved away from the pulp fibres.

it here the amounts of dense hard woods used in admixture with poplar wood are increased to a greater extent, for example, to :1 amount similar to that of the poplar wood, the problem is presented of treating a charge which, in total weight of wood, may be halt as much again as the weight of the ordinary charge of poplar wood in a digester of the same size. woods, such as beech, birch and maple, etc., are treated by themselves, either separately or in admixture with one another, the total weight ot the wood will be radically greater than the weight of poplar wood, normally chargeable into the same. digester. The weight of the hard woods may be as much as twice that oi the poplar wood, while the amounts oli non-fibrous constituents which must be separated from the fibres may be even greater in proportion, because of the lesser content of fibres and the increased content of non-fibrous constituents which certain ot the dense hard woods contain.

When the dense hard woods are cooked by themselves, the cooking liquor will require to be greatly increased in strength, in order that a digester full of the hard wood chips may be satisfactorily cooked, and it may advantageously be increased in amount, as compared with the amount uscd with poplar wood. It is an advantage of the present invention, however, that even these dense woods can be cooked, either by themselves or in admixture with varying amounts of poplar (and similar) wood. \Vith these \Vhcre the dense hard dense woods, however, the same ratio ot caustic soda to sodium sulphite need not ordinarily be used that would be used in the treatment of poplar wood. In general, the increase in cooking reagents may be made up, for the most part, of .sodium sulphite, so that in any case, the amount and strength of caustic soda in the composite cooking liquor is kept below the amount which will cause any considerable injury to the fibres of the pulp produced. For example, with dense hard wood the cooking liquor may be made up of caustic soda and sodium sulphite in approximately equal amounts, so far as their sodium content is concerned, and such a composite cooking liquor can be used of a strength somewhat less than double the strength of a cooking liquor which would be similarly used in the treatment of poplar wood, and in somewhat increased amounts, although the amounts and strengths of the cooking liquor can be somewhat varied as well as the proportions of caustic soda and sodium sulphite which the cooking liquor contains. 111 cooking heavy hardwoods it is desirable to increase the volume above the amount used with poplar wood.

In cookingmixtures of poplar wood and dense hard woods, where the poplar wood not the predominating wood, the strengths and amounts of the reagents in the cooking liquor can be regulated and controlled in accordance with the amounts of non-fibrous materials which the woods contain, while maintaining the caustic soda of a strength and concentration which will. avoid any considerable injury to the pulp fibres, and making up the balance of the cooking reagents mostly of sodium sulphite.

Even where different woods are cooked in admixture with each other, the present invention enables the different woods to be satisfactorily cooked without over-cooking part of the wood while completing the cooking of the rest, which may require a somewhat shorter time. By cooking mixed woods in this way, mixed pulps may be directly produced containing fibres of different charac teristics produced from different woods. lVe have found that the fibres from different woods possess different properties and characteristics which enable them to be distinguished from each other as well from fibres produced, forexample, from poplar wood by the ordinary soda process.

The residual liquors produced in the new process of the present invention can be readily treated for the regeneration of the cooking liquors by subjecting them to evaporation in multiple effect evaporator-s and by calcining the resulting concentrated liquor in rotary calcining furnaces such as are used in the calcining of black liquor from the ordinary soda process. Owing to the decreased amount of wood substance contained newness in solution in the residual liquors from poplar wood), the liquors are less gummy in character and give less trouble in the evaporators from foaming or gumming, etc. The liquor, from the strong liquor tank, of a strength of around 14 to 14.5 iwzddell at a temperature of 155 to 160 F. can be read ily concentrated in quadruple effect evaporators to or l waddell, or even high-u", at a temperature of M0 to M4 1*. the concentrated liquor can then be fed to the ru tary calcining furnaces such as are used in treating black liquors from the ordinary soda process.

We have found, that, although the residual liquors contain a considerable amount oi combined sulphur they can nevertheless be calcined in the rotary furnaces without driw ing off the entire amount of the combined sulphur. lVe have also found that under certain conditions sodium sulphite comes from the rotary calcining furnaces without any considerable amount of reduction by the admixed organic matter, a few per cent. only of sulphide being formed. T he presence of a few per cent of sodium sulfide is, however, advantageous in the cooking liquor, supplementing the action of the caustic soda and of the sodium sullite. The rotary calcinmg furnaces may, for example, have a di ameter of about 9 f et and a length of about 16 feet and may be heated by coal fire. The concentrated residual liquor from the multiple effect evaporators, concentrated to about (SO-65 Twaddell can be fed into the rotary furnaces at one endand the calcined product discharged at the other. l i' 'th proper control of the calcination, such that fusion of the discharged product avoided much as possible, the sulphite comes from the furnace in considerable amount.

1 The calcined product can then be leached. tor example, by introducing it into water and agitating the water, or by otherwise carrying out the leaching operation. By counteicurrent leaching a solution can be obtained up to 23 'lwaddell. This liquor can be subjected to causticizing with lime to convert its contained sodium carbonate for the most part into caustic soda, using for example, 53 or 54s parts of calcium oxide to 100 parts of sodium carbonate. The sulphite contained in the liquor is preferably not causticized, and the amount of lime should be kept sufliciently low to avoid this. The causticizing operation can be carried out by heating and agitating for a suilicient period of time to carry the causticizing to the desired degree. Some sodium carbonate will usually be left uncausticized in the resulting liquor, which will be made up for the most part of caustic soda, resultii from the cansticizing operation, and diuin sulphite. some small and incidental amount of sodium sulphide may also be present, produced during the calcination, but we have found that, by avoiding smelting of the charge during calcination, there is no building up of sulphide to an objectionable degree nor is there any excessive building up of sulphate, but the sulphite in consider-aide part passes through the turnace and is recovered for further use, while such small and incidental amounts of sodium sulphide as may be formed and as may be present in the regenerated liquor, are ithout any objectionable effect in the process when carried out with the regenerated cooking liquor, although such amounts of sodium sulphide can be readily removed. if desired. Such amounts of sodium sulfide as are incidentally produced during the regeneration will when present. SUPPlOHlOHt the action of the caustic soda and sodium sultite, giving a composite cooking liquor containing caustic soda, sodium sullite and sodium sulfide, with the caustic soda in prepondcrating amount.

In order to make up for losses of caustic soda and sodium sulphite, a suitable amount of dry soda ash, for example, may be added to the liquor before causticizing, while the necessary amount of sodium sulphite can be readily produced, for example, by burning sulphur in a small sulphur burner and absorbing the sulphur dioxide in a solution of soda ash or a solution which contains the sodium carbonate leached from the calcined product above described. A convenient method of supplying sodium sulphite in the required amount is to absorb the sulphur dioxide from a sulphur burner in an absorp tion tower through which a solution of sodium carbonate is circulated containing arounc 130 to 140 grams of soda ash per liter. or a part at the leach-liquor can be similarly used. The freshly made sodium sulphite solution may be added to the remainder of the cooking liquor either in the digester or before it enters the digester. The regenerated cooking liquor may be sep: rately introduced into the digester and the newty made sulphite liquor separately added. for example, adding 394: cubic feet of regenerated cooking liquor of 16 T waddell at (30 F. together with about (36 cubic iteet of freshly made sodium sulgiihite liquor oi. proper strength, this referring especially to poplar wood. Some residual liquor from a previous operation may be substituted for an equal volume of water so that the total volume added remains about 460 cubic feet for the particular digester specified.

The cooking liquors thus produced can be used in carrying out the cooking operation hereinbetore described.

When dense hard woods are treated (for example birch, beech, maple, etc.) which have a considerably greater weight than poplar wood, the amount of non-fibrous constituents which the woods contain and which must be removed by the cooking operation will be radically greater than in the case of poplar wood, assuming that a digestcr full of the wood is treated in each case. Along with the greatly increased amount of pulp which can be produced from a digcstcr charge of the hard woods, there will be a similar increase, or even a greater increase, in the amount of non-fibrous constituents present in the residual liquors, particularly where the hard woods have a considerably ii'icreased per cent of non-fibrous constitucuts as con'ipared with poplar wood. The re sidual liquors will accordingly contain a greatly increased content both of organic and ot inorganic constituents, such as combined sodium organic compounds and sulpho-organic compounds, etc. These residual liquors, of such increased concentration, can be somewhat diluted by admixture with wash waters, but dilution to an objectionaljilc degree can be readily prevented and the treatment of the more concentrated liquors; presents added advantage because of the decreased amount of water to be removed and the radically increased concentration of the constituents which the liquor contains. The. treatment of the liquor can, however, be car-- ried out in a manner similar to that above described in connection with the treatn'ient of residual liquors from the cooking of poplar wood.

It will thus be seen that the present invention provides a regenerative process of pulp manufacture in which the cooking liquor is of a composite character, containing essentially caustic soda and sodium sulphite, and in which the residual liquors can nevertheless be rcadily treated for the regeneration therefrom of the cooking liquor containing essentially the same ingredients. The process, when thus carried out as a regenerative. process, is of a cyclic character, with cooking of the wood chips with the composite cooking liquor, evaporation of the residual liquor and calcination ot the concentrated liquor, with regulation of the calcining opera-- tion, so that the chemicals are recovered without excessive loss, and with lean-hing o l? the calcined material and caustieizing oi the leached liquor with lime, using a regulated amount of lime. such that the major portion of the sodium carbonate is causticized.

From one view point, the process of the present invention has features of similarity with the ordinary soda process, particularly in that the cooking liquor contains caustic soda as one of its characteristic ingredients. From the ordinary soda process. however, the process of the present invention is distinguished in many important respects, hereinbetore referred to. The cooking liquor. although it contains caustic soda as one of its essential constituents, nevertheless has a put sufiiciently mild action upon the wood due to the reduced amount and concentration oi? sodium hydroxide so that the objections of the ordinary soda process are largely avoided; while the use of a composite cooking liquor enables important additional advantages to be obtained. The present process retains inany oi the advantages of both the soda process and the acid sulphite process, while avoiding the strongly acid character of the latter and the objectionable alkaline strength of the cooking liquor of the former. The residual liquor produced according to the present invention is also of distinctive and characteristic c m1position. It contains less dissolved l'ibrous material and conse intently less organic n'iatter. It can be more readily evaporated without ijliliiculty; and it acts in a charzmteristic way when subjected to calcination, and when the calciningg operation is regulated in the manner above described. From the calcined material the new cooking liquor an be produced by regulated causticizing operation, regulated and controlled in the manner above indicated.

The pulp produced according; to the present invention also is of an improved character and has fibres which diller in their composition and properties lrom those produced by the ordinary soda process. The improved properties of the fibre distinguish it in its handling throughout the mill, in the manner above describechand this improvement is noticeable in generalmill operations. The pulp has a characteristic feel, has increased strength and is characterized .by llreat uniformity While it runs .freely through the mill, and paper made therefrom is safer in its production, while the paper produced has the improved and distinguishinp; properties above described. The process of the present invention, accordingly, presents advantages throughout the entire mill operations of a pulp and paper mill. as compared with a mill (n eratinp; the soda process and employing admixed soda and sulphite pulp for the manufacture of paper. The present invention makes it possible to eliminate the admixture of long fibre ,sulphite pulp with soda pulp for the manufacture oi the heavier weights of book paper, while the paper produced according; to the present invention is itself of improved quality.

-J'\ mill designed and constructed for the carrying out of :the soda pulp process e. g, with poplar wood, can be transformed into a mill for carrying out the improved process of the present invention for, treating pop lar wood with few changes. The same equipment can housed in substantially the same manner in which it is now used in carrying out the soda. process; but the carrying out of the present process will nevertheless result in a radical improvementin the operation of the mill, not only in the yieldol' pulp produced from the same amount of wood, but also in the ease with which the mill can be operated and kept in balance, vith successive parts of the mill operating on schedule and in the improved quality and character of the products produced, i. e., residual liquor, pulp and paper. The improvements in the operation of the mill, as compared with the operation of the same mill with the soda process, are sulliciently marked so that they are noticeable even to the workmen throughout the mill, so that the worlnnen can readily tell the dillerence in the pulp by its feel and by the manner in which it can be handled and by the prodnot produced.

in transforming a mill, operating accordj to the soda. process, for example, with V -,plar wood, into a mill operating. according; to the present invention, the transition is readily made.

white an be gradually introduced iuto'the cooking; liquor of one of a group oi digesters, or into several dig-esters 01' the group, and, with theregeneration and recovery of sodium sulphite from the residual liquors, and the addition oi"? further. amounts of sodium sulphit-e, theamount of sodium sulphite can be gradually built up to the desired extent, and thereafter niiaintain-ed by the addition of such i urther amounts as may be necessary to make up for losses.

its the amount of sodium sulphite builds up in this way, the improvement in the pulp and in the handling of the pulp through the mill becomes noticeable even before the amount of sodium sulphite is increased to that which may finally be used in the process. A few per cent only of added sodium sulphite, with corresponding reduction in the amount of: caustic soda, has noticeable ellect in improving; the proce s. while an For example, sodium sul ill) amount of sodium sulphite corresponding to about 10 per cent oil the caustic soda, and with a corresponding reduction in caustic soda, results in an improvement in operations so radical in character that those operating the process can immediately notice it throughout the mill operations, and so that the yield in pulp produced will be increased to a considerable extent. The inun'ovement will be noticeable, for example, in the color of the unbleached pulp, which, instead of being a dark brown. will have a reddish or a pinkish cast, well as in the brightness of the pulp and the whiteness of: the bleached pulp, itbeinp; necessary in some instances of paper manufacture to add coloring material in the production o'l'f ordinary white paper because of the unusual whiteness of the bleached pulp as compared with the standard product for which the pulp was to be used.

lVhere book and magazine paper mills using pulp produced by the soda process have heretofore been obliged to purchase or produce long fibre sulphite pulp (made by the acid sultite process) at an increased cost (as compared with the value of soda pulp) in order to admin the suli'itc and soda pulps to give a paper of the necessary quality and strength, the present invention enables the purchase or production of sulphiie pulp to be eliminated, or reduced to a minimum, and enables an improved paper to be produced solely from short fibre woods, e. g. poplar, without any admixture whatever oflong fibres therewith. il here mills now operate both the soda and the acid sulphite processes in order to manufacture the two kinds of pulp for admixture with each other, the present invention enables the plant to be readily converted in part or in whole to the improved process which makes unnecessary the manufacture of two different kinds of pulps for admixture and which enables the mill to operate with a wider variety of woods which cannot be readily treated according to the common methods. In fact, the wider range of application of the present invention is an important and characteristic advantage, inasmuch as it greatly extends the range of available woods for the manufacture of satisfactory pulp. and makes unnecessary the treatment of the more expensive pulp woods which are decreasing in available amount and correspondingly increasing in cost.

The present invention accordingly pre sents many and varied advantages which are largely cumulative in character and which include a wider range of application and of materials treated as well as improvements in the method of treatment and throughout the method of treatment, and in the products which the process produces.

We claim:

1. The method of manufacturing pulp from wood which comprises cooking the wood under pressure with a cooking liquor containing caustic soda and sodium sulphite as its primary reagents, the amount of the sulphite not exceeding that of the caustic soda.

2. The method of manufacturing pulp from wood which comprises cooking the wood under pressure with a cooking liquor containing a preponderating amount of caustic soda and a lesser amount oi sodium sulphite.

3. he method of manufacturing pulp from wood which comprises cooking the wood under pressure with a cooking liquor containing a preponderating amount of caustic soda and an amount of sodium sulphite equivalent to about 10 to 25% of the amount of caustic soda.

4:. The method of manufacturing pulp from wood which comprises cooking the wood under pressure with a cooking liquor containing a preponderating amount of caustic soda and a lesser amount of sodium sulphite, separating the residual liquor from the pulp, concentrating the residual liquor, and calcining the concentrated liquor to carbonize organic matter, leaching the calcined material, and causticizing the resulting solution to give a composite solution containing caustic soda and sodium sulphite.

5. The method of manufacturing pulp from wood which comprises cooking the wood under pressure and at an elevated temperature, with a cooking liquor containing caustic soda, sodium sulfite and sodium sulfide, the caustic soda being present in preponderating amount.

6. The regenerative method of manufacturing pulp from wood which comprises cooking the wood under pressure with a cooking liquor containing a preponderating amount oi, caustic soda and a lesser amount of sodium sulfite, separating the residual liquor from the pulp, subjecting the residual liquor to concentrating and, calcining operations, dissolving the soluble compounds, and treating the resulting solution for the production of further amounts of cooking liquor, said treatment including a causticizing treatment.

7. The regenerative method of manufacturing pulp from wood which comprises cooking the wood under pressure with a cooking liquor containing a preponderating amount of caustic soda and a lesser amount of sodium sulfite, separating the residual liquor from the pulp, subjecting the residual liquor to concentrating and calcining operations, dissolving the soluble compounds, and treating the resulting solution for the production of further amounts of cooking liquor, said treatment including a causticizing treatment and the formation or" additional sodium sulfite.

8. The regenerative method of manufacturing pulp from wood which comprises cooking the wood under pressure with a cooking liquor containing a preponderating amount of caustic soda and a lesser amount of sodium sulfitc, separating the residual liquor from the pulp, subjecting the residual liquor to concentrating and calcining operations, the calcination being regulated to give a calcined product containing sodium carbonate and sodium sultite, dissolving the soluble compounds and incompletely caustieizing the same to reproduce a solution containing caustic soda and sodium sulfite for further use in the cooking process.

9. The regenerative method of pulp manu t'acture which comprises cooking the wood under pressure with a cooking liquor containing a preponderating amountv of caustic soda and lesser amounts of sodium sulfite and sodium sulfide, separating the residual liquor from the pulp, concentrating the residual liquor, calcining the conceutrated liquor under conditions to form some sodium sulfide, dissolving the soluble compounds, and trey 'ng the some to 'loriiu furl-her amounts of cooking liquor, said treatment sodium sultite, and the cooking- OpOldlllOH being carried out'under a steam pressure of around 110 to 120 poun'" 11. The method 'oct 1nenuitacturing pulp from wood which comprises cook ng; the wood under pressure and at on elevr d temperature with a cooking liquor containing caustic soda in preponderating; en'iount and i also containing; sodirun suli'itc m such amount that it represents from '10 to substantially 25% the total sodium pre ent.

12. The method. of inanutactur-iuq pulp from Wood which comprises cooking the Wood under pressure and stun elevated tein--- perature with a cooking; liquor containing;- about 50 to 60 grams per liter of caustic soda and about 10 to 25 grams per liter of normal sodium sulfite.

13. The method. oi nm from Wood which COlllDl'lSQw suhieo WOOCl to a cooking operation under pro, at an elevated temperature with a cool; liquor containing a preponderatin j z'uuornt of caustic soda, together with :1 smaller amount of sodium sultlte, and containing sodium carbonate, the cooking operation being carried out with relief oi ,o'ascs 'tlOEll the top of the digester 'LT'ODJ time to time during the cooking operation.

14;. As new product, a pulp result ng" from the cooking oi Wood With a cou'ipo .c cooking liquor containing a prepcuderatine; amount of caustic soda and a lesser uinznnit of sodium sulphite, said pulp coul'uiuij libres of great uniformity and heinoj tr e tl owin l5. As a new product,

pulp resulting troni the cooking of short fibre Wood wi h a composite cooking liquor ctmtanuuo; a preosses lihres ot radically increased strength as compared with librcs resulting from the cooking o'l poplar wood by the ordinary soda process, and said pulp perniiitting the manufacture of superior paper therefrom Without the admixture of long libre pulp therewith.

11''. As a new product, a paper made on tlrely of short lihre pulp resulting from the cooking of slimrtdiln'e W()O(l with a coniposite cooking liquor containing a preponderating: amount of *aust-ic soda and a lesser amount 0t sodium sulphite.

18. As a new product, a paper made up entirely of poplar pulp (which may contain a small admixture of bass W00(l pulp) produced with a cooking liquor containing a preponderotinp; amount of caustic soda and alesser amount of sodium sulphite.

19. A resid rel liquor resulting from the cooking of Wood with a composite cookingliquor containing a preponderating amount of caustic soda and a lesser amount of so- (lllllll sulphite.

:20. As a new product, a paper made ontirely of short fiber pulp, the short fiber pulp resulting: from the cooking' of short fiber u'ooil .h a cooking liquor containing a preponderaling aniount of caustic soda and a lesser amount of sodium sulfite.

As a new product a paper comprisll 2; short fiber pulp resulting; from the cooking 0t shorhfiher Wood with a composite cooking; liquor containing a pi'eponderating u tot caustic soda and a lesser amount oi sodium sulphite.

its a new product, a paper comprising p per pulp containing fibers otsubstantially unuioriu length. and properties produced by cooking the wood with a cooking liquor coutsining a preponderating amount of caustic soda and a lesser amount of sodium suliite.

23. As a new product, a paper made from short fiber pulp admixed with a small amount of lon fiher pulp, the short liber pulp rcsi'lltinp iron] the cooking" of short .lihcr wood with a'cooltinp; liquor containing a prepondcratiuo' amount ot caustic soda and a less tll'llfillll'f'fi'f sodiuni sullite.

24:. The ll'ltlllfltl o't i'i'ianu'l acturing pulp tron: wood which comprises cooking the wood under lll'tF-iS-YHHY and at an elevutm'l'tcmperuture with a cooking liquor containing sodc c bin-ed as sodiuiu hydrox de and a lesser amount oi soda combined as sodium white and also including an :u'uount oil. sir =iuiu sullid which is less than the amount oi soda .iii sullite.

95. llhe me hod ot uianulacturing: pulp Wood which comprises tre ting Wood means ot a liquor coutoiningrsode as so combined as sodium sulfite sud asnsodiuin sulfide, the amount of sodium sulflte being atlesst about ten percent (10%) ot the amount sodium hydroxid oxide and lesser amounts oi: soda lll 26. The method of manufacturing pulp which comprises treating cellulose-fibre-bearing material, including lignified material, by means of liquor containing soda combined as sodium hydroxide and lesser amounts of soda combined as sodium sulfite and as sodium sulfid, the amount of sodium sulfite being at least about ten percent (10%) of the amount of sodium hydroxide, and the amount of sodium sulfid being less than the amount of the sodium sulfite.

27. In a process for producing pulp from wood, the steps which include subjecting wood to a digesting treatment by means of liquor supplied with soda combined as sodium hydroxide and as sodium sulfite, the amount of sodium sulfite being at least about ten percent (10%) of the amount of the sodium hydroxide, and containing digestive material, exclusive of the sodium sulfite, alkaline to phenolphtalein, in an amount which is capable of digesting at least onehalf of the non-fibrous organic content of the wood, and the digestion treatment being conducted so that fibres of the resulting material are readily separable from each other by mechanical treatment.

28. In a process for producing pulp from wood, the steps which include subjecting wood to a digesting treatment by means of liquor supplied with soda combined as sodium hydroxide and as sodium sulfite, the amount of sodium sulfite being at least about ten percent (10%) of the amount of the sodium hydroxide, and containing digestive material, exclusive of the sodium sulfite, alkaline to phenolphtalein, in an amount which is capable of digesting at least onehalf of the non-fibrous organic content of the wood, and the digesting treating being conducted so as to separate from the fibres substantially all non-fibrous organic constituents without unduly weakening or injuring the resulting fibres.

29. In a process for producing pulp from wood, the steps which include subjecting wood to a digesting treatment by means of liquor supplied with soda combined as sodium hydroxide and lesser amounts of soda combined as sodium sulfite and sodium sultid. the amount of sodium sulfite being at least about ten percent (10%) oi the amount of sodium hydroxide, and the amount of sodium hydroxide being less than would be required to digest a similar amount of the nontibrous organic content of the wood if sodium hydroxide were the only reagent employed.

30. In a process for producing pulp from wood, the steps which include subjecting wood to a digesting treatment by means of liquor supplied with soda combined as sodium hydroxide and as sodium sulfite, the amount of sodium sulfite being at least about ten percent (10%) of the amount of the sodium hydroxide, and the hydroxide being supplied in an amount which is capable of digesting at least one-half of the non-fibrous organic content of the wood.

31. In a process for producing pulp from wood, the steps which include subjecting wood to a digesting treatment by means of liquor supplied with soda combined as sodium hydroxide and as sodium sulfite, the amount of sodium sulfite being at least about ten percent (10%) of the amount of the sodium hydroxide, and the hydroxide being supplied in an amount which is capable of digesting at least one-half of the non-fibrous organic content of the wood, and the digesting treatment being conducted so that fibres oi the resulting material are readily separable from each other by mechanical treatment, and the separated fibres are relatively strong as compared with chemical pulp from the same kind and quality of wood as produced by the conventional soda process.

32. In a process for producing pulp, the steps which include subjecting cellulosebearing material, including ligneous material, to a digestion treatment by means of liquor supplied with alkali combined as alkali hydroxide, as alkali sulfite and as alkali sulfid, the amount of the alkali sulfite being at least as large as the amount of the alkali sulfid, and the hydroxide being supplied in an amount which is capable of digesting at least one-hall of the non-fibrous organic content of the cellulose-bearing material.

33. In a process for producing pulp from wood, the steps which include subjecting wood to a digestion treatment by means of liquor supplied with soda combined as sodium hydroxide, as sodium sulfite and as sodium sulfid, the amount of the sodium sulfite being at least as large as the amount of the sodium sulfid, and the hydroxide being supplied in an amount which is capable of digesting at least one-half of the non-fibrous organic content of the wood, and the digestion treatment being conducted so as to render fibres ol the resulting material readily separable from each other by mechanical treatment, and the resulting fibres being sufficiently free from nou-filn'ous organic material and of sufiicient strength to be employed in the formation of the fibrous structure of machine-made paper weighing between 30 and 70 pounds per ream of 500 sheets, each 25 inches by 38 inches.

In testimony whereof we affix our signatures.

LINN BRADLEY. EDWARD P. MCKEEFE. 

